How to change the tax amount in quote

Question

I wish to change the tax amount in checkout programmatically I am using following code let me know If I am making any mistake.

$session= Mage::getSingleton("checkout/session");
$quote_id = $session->getQuoteId();
$quote = Mage::getModel("sales/quote")->load($quote_id);
$items = $quote->getAllItems();
foreach($items as $item) { 
   $item->setTaxAmount(0);
   $item->setBaseTaxAmount(0);
   $item->setPriceInclTax($value);
   $item->setBasePriceInclTax($value);
   $item->save();
   $quote->save();
}

Answer 1

After Long research and trials Finally I come up with this solution.

$finalPrice = $product->getPrice();
    $item = Mage::getSingleton('checkout/session')->getQuote()->getItemByProduct($product);
    $finalprice = $finalPrice - $item->getTaxAmount();
    $quote = Mage::getModel('checkout/session')->getQuote();
    $address = $quote->getShippingAddress();
    if ($address)
    {   $address->setSubtotalInclTax($finalprice);
        $product->setTaxClassId(0);
        $product->setPrice($finalprice);

     }